@article{GoettenHavermannBraunetal.2020, author = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees}, title = {Wind-tunnel and CFD investigations of UAV landing gears and turrets - Improvements in empirical drag estimation}, series = {Aerospace Science and Technology}, volume = {107}, journal = {Aerospace Science and Technology}, number = {Art. 106306}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1270-9638}, doi = {10.1016/j.ast.2020.106306}, year = {2020}, abstract = {This paper analyzes the drag characteristics of several landing gear and turret configurations that are representative of unmanned aircraft tricycle landing gears and sensor turrets. A variety of these components were constructed via 3D-printing and analyzed in a wind-tunnel measurement campaign. Both turrets and landing gears were attached to a modular fuselage that supported both isolated components and multiple components at a time. Selected cases were numerically investigated with a Reynolds-averaged Navier-Stokes approach that showed good accuracy when compared to wind-tunnel data. The drag of main gear struts could be significantly reduced via streamlining their cross-sectional shape and keeping load carrying capabilities similar. The attachment of wheels introduced interference effects that increased strut drag moderately but significantly increased wheel drag compared to isolated cases. Very similar behavior was identified for front landing gears. The drag of an electro-optical and infrared sensor turret was found to be much higher than compared to available data of a clean hemisphere-cylinder combination. This turret drag was merely influenced by geometrical features like sensor surfaces and the rotational mechanism. The new data of this study is used to develop simple drag estimation recommendations for main and front landing gear struts and wheels as well as sensor turrets. These recommendations take geometrical considerations and interference effects into account.}, language = {en} } @article{GoettenHavermannBraunetal.2020, author = {G{\"o}tten, Falk and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees}, title = {Improved Form Factor for Drag Estimation of Fuselages with Various Cross Sections}, series = {Journal of Aircraft}, journal = {Journal of Aircraft}, publisher = {AIAA}, address = {Reston, Va.}, issn = {1533-3868}, doi = {10.2514/1.C036032}, pages = {1 -- 13}, year = {2020}, abstract = {The paper presents an aerodynamic investigation of 70 different streamlined bodies with fineness ratios ranging from 2 to 10. The bodies are chosen to idealize both unmanned and small manned aircraft fuselages and feature cross-sectional shapes that vary from circular to quadratic. The study focuses on friction and pressure drag in dependency of the individual body's fineness ratio and cross section. The drag forces are normalized with the respective body's wetted area to comply with an empirical drag estimation procedure. Although the friction drag coefficient then stays rather constant for all bodies, their pressure drag coefficients decrease with an increase in fineness ratio. Referring the pressure drag coefficient to the bodies' cross-sectional areas shows a distinct pressure drag minimum at a fineness ratio of about three. The pressure drag of bodies with a quadratic cross section is generally higher than for bodies of revolution. The results are used to derive an improved form factor that can be employed in a classic empirical drag estimation method. The improved formulation takes both the fineness ratio and cross-sectional shape into account. It shows superior accuracy in estimating streamlined body drag when compared with experimental data and other form factor formulations of the literature.}, language = {en} } @inproceedings{GoettenFingerHavermannetal.2020, author = {G{\"o}tten, Falk and Finger, Felix and Havermann, Marc and Braun, Carsten and Marino, Matthew and Bil, Cees}, title = {Full Configuration Drag Estimation of Small-to-Medium Range UAVs and its Impact on Initial Sizing Optimization}, series = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020}, booktitle = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020}, year = {2020}, language = {en} } @article{GossmannThomasHorvathetal.2020, author = {Gossmann, Matthias and Thomas, Ulrich and Horv{\´a}th, Andr{\´a}s and Dragicevic, Elena and Stoelzle-Feix, Sonja and Jung, Alexander and Raman, Aravind Hariharan and Staat, Manfred and Linder, Peter}, title = {A higher-throughput approach to investigate cardiac contractility in vitro under physiological mechanical conditions}, series = {Journal of Pharmacological and Toxicological Methods}, volume = {105}, journal = {Journal of Pharmacological and Toxicological Methods}, number = {Article 106843}, publisher = {Elsevier}, address = {New York, NY}, doi = {10.1016/j.vascn.2020.106843}, year = {2020}, language = {en} } @incollection{GollandOhrtmann2020, author = {Golland, Alexander and Ohrtmann, Jan-Peter}, title = {Video surveillance: The supervisory authorities' view andrecent case law}, series = {Turning Point in Data Protection Law}, booktitle = {Turning Point in Data Protection Law}, publisher = {Nomos}, address = {Baden-Baden}, isbn = {978-3-8487-6909-4}, doi = {10.5771/9783748921561-175}, pages = {175 -- 178}, year = {2020}, language = {en} } @incollection{Golland2020, author = {Golland, Alexander}, title = {Struggling with users' consent: Economic approach to solve the issue of coupling}, series = {Turning Point in Data Protection Law}, booktitle = {Turning Point in Data Protection Law}, publisher = {Nomos}, address = {Baden-Baden}, isbn = {978-3-8487-6909-4}, doi = {10.5771/9783748921561-121}, pages = {121 -- 126}, year = {2020}, language = {en} } @article{GerhardsSanderZivkovicetal.2020, author = {Gerhards, Michael and Sander, Volker and Zivkovic, Miroslav and Belloum, Adam and Bubak, Marian}, title = {New approach to allocation planning of many-task workflows on clouds}, series = {Concurrency and Computation: Practice and Experience}, volume = {32}, journal = {Concurrency and Computation: Practice and Experience}, number = {2 Article e5404}, publisher = {Wiley}, address = {Chichester}, issn = {1532-0634}, doi = {10.1002/cpe.5404}, pages = {1 -- 16}, year = {2020}, abstract = {Experience has shown that a priori created static resource allocation plans are vulnerable to runtime deviations and hence often become uneconomic or highly exceed a predefined soft deadline. The assumption of constant task execution times during allocation planning is even more unlikely in a cloud environment where virtualized resources vary in performance. Revising the initially created resource allocation plan at runtime allows the scheduler to react on deviations between planning and execution. Such an adaptive rescheduling of a many-task application workflow is only feasible, when the planning time can be handled efficiently at runtime. In this paper, we present the static low-complexity resource allocation planning algorithm (LCP) applicable to efficiently schedule many-task scientific application workflows on cloud resources of different capabilities. The benefits of the presented algorithm are benchmarked against alternative approaches. The benchmark results show that LCP is not only able to compete against higher complexity algorithms in terms of planned costs and planned makespan but also outperforms them significantly by magnitudes of 2 to 160 in terms of required planning time. Hence, LCP is superior in terms of practical usability where low planning time is essential such as in our targeted online rescheduling scenario.}, language = {en} } @inproceedings{GeibenGoettenHavermann2020, author = {Geiben, Benedikt and G{\"o}tten, Falk and Havermann, Marc}, title = {Aerodynamic analysis of a winged sub-orbital spaceplane}, series = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020}, booktitle = {Deutscher Luft- und Raumfahrtkongress - DLRK 2020}, year = {2020}, language = {en} } @article{GazdaMaurischat2020, author = {Gazda, Quentin and Maurischat, Andreas}, title = {Special functions and Gauss-Thakur sums in higher rank and dimension}, publisher = {De Gruyter}, address = {Berlin}, pages = {26 Seiten}, year = {2020}, language = {en} } @article{Gaigall2020, author = {Gaigall, Daniel}, title = {Hoeffding-Blum-Kiefer-Rosenblatt independence test statistic on partly not identically distributed data}, series = {Communications in Statistics - Theory and Methods}, volume = {51}, journal = {Communications in Statistics - Theory and Methods}, number = {12}, publisher = {Taylor \& Francis}, address = {London}, issn = {1532-415X}, doi = {10.1080/03610926.2020.1805767}, pages = {4006 -- 4028}, year = {2020}, abstract = {The established Hoeffding-Blum-Kiefer-Rosenblatt independence test statistic is investigated for partly not identically distributed data. Surprisingly, it turns out that the statistic has the well-known distribution-free limiting null distribution of the classical criterion under standard regularity conditions. An application is testing goodness-of-fit for the regression function in a non parametric random effects meta-regression model, where the consistency is obtained as well. Simulations investigate size and power of the approach for small and moderate sample sizes. A real data example based on clinical trials illustrates how the test can be used in applications.}, language = {en} } @article{Gaigall2020, author = {Gaigall, Daniel}, title = {Testing marginal homogeneity of a continuous bivariate distribution with possibly incomplete paired data}, series = {Metrika}, volume = {2020}, journal = {Metrika}, number = {83}, publisher = {Springer}, issn = {1435-926X}, doi = {10.1007/s00184-019-00742-5}, pages = {437 -- 465}, year = {2020}, abstract = {We discuss the testing problem of homogeneity of the marginal distributions of a continuous bivariate distribution based on a paired sample with possibly missing components (missing completely at random). Applying the well-known two-sample Cr{\´a}mer-von-Mises distance to the remaining data, we determine the limiting null distribution of our test statistic in this situation. It is seen that a new resampling approach is appropriate for the approximation of the unknown null distribution. We prove that the resulting test asymptotically reaches the significance level and is consistent. Properties of the test under local alternatives are pointed out as well. Simulations investigate the quality of the approximation and the power of the new approach in the finite sample case. As an illustration we apply the test to real data sets.}, language = {en} } @article{Gaigall2020, author = {Gaigall, Daniel}, title = {Rothman-Woodroofe symmetry test statistic revisited}, series = {Computational Statistics \& Data Analysis}, volume = {2020}, journal = {Computational Statistics \& Data Analysis}, number = {142}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0167-9473}, doi = {10.1016/j.csda.2019.106837}, pages = {Artikel 106837}, year = {2020}, abstract = {The Rothman-Woodroofe symmetry test statistic is revisited on the basis of independent but not necessarily identically distributed random variables. The distribution-freeness if the underlying distributions are all symmetric and continuous is obtained. The results are applied for testing symmetry in a meta-analysis random effects model. The consistency of the procedure is discussed in this situation as well. A comparison with an alternative proposal from the literature is conducted via simulations. Real data are analyzed to demonstrate how the new approach works in practice.}, language = {en} } @inproceedings{FrantzBinderBuschetal.2020, author = {Frantz, Cathy and Binder, Matthias and Busch, Konrad and Ebert, Miriam and Heinrich, Andreas and Kaczmarkiewicz, Nadine and Schl{\"o}gl-Knothe, B{\"a}rbel and Kunze, Tobias and Schuhbauer, Christian and Stetka, Markus and Schwager, Christian and Spiegel, Michael and Teixeira Boura, Cristiano Jos{\´e} and Bauer, Thomas and Bonk, Alexander and Eisen, Stefan and Funck, Bernhard}, title = {Basic Engineering of a High Performance Molten Salt Tower Receiver System}, series = {Solar Paces 2020}, booktitle = {Solar Paces 2020}, pages = {1 -- 10}, year = {2020}, language = {en} } @article{FrankoDuKallweitetal.2020, author = {Franko, Josef and Du, Shengzhi and Kallweit, Stephan and Duelberg, Enno Sebastian and Engemann, Heiko}, title = {Design of a Multi-Robot System for Wind Turbine Maintenance}, series = {Energies}, volume = {13}, journal = {Energies}, number = {10}, publisher = {MDPI}, address = {Basel}, issn = {1996-1073}, doi = {10.3390/en13102552}, pages = {Article 2552}, year = {2020}, abstract = {The maintenance of wind turbines is of growing importance considering the transition to renewable energy. This paper presents a multi-robot-approach for automated wind turbine maintenance including a novel climbing robot. Currently, wind turbine maintenance remains a manual task, which is monotonous, dangerous, and also physically demanding due to the large scale of wind turbines. Technical climbers are required to work at significant heights, even in bad weather conditions. Furthermore, a skilled labor force with sufficient knowledge in repairing fiber composite material is rare. Autonomous mobile systems enable the digitization of the maintenance process. They can be designed for weather-independent operations. This work contributes to the development and experimental validation of a maintenance system consisting of multiple robotic platforms for a variety of tasks, such as wind turbine tower and rotor blade service. In this work, multicopters with vision and LiDAR sensors for global inspection are used to guide slower climbing robots. Light-weight magnetic climbers with surface contact were used to analyze structure parts with non-destructive inspection methods and to locally repair smaller defects. Localization was enabled by adapting odometry for conical-shaped surfaces considering additional navigation sensors. Magnets were suitable for steel towers to clamp onto the surface. A friction-based climbing ring robot (SMART— Scanning, Monitoring, Analyzing, Repair and Transportation) completed the set-up for higher payload. The maintenance period could be extended by using weather-proofed maintenance robots. The multi-robot-system was running the Robot Operating System (ROS). Additionally, first steps towards machine learning would enable maintenance staff to use pattern classification for fault diagnosis in order to operate safely from the ground in the future.}, language = {en} } @inproceedings{FingerdeVriesVosetal.2020, author = {Finger, Felix and de Vries, Reynard and Vos, Roelof and Braun, Carsten and Bil, Cees}, title = {A comparison of hybrid-electric aircraft sizing methods}, series = {AIAA Scitech 2020 Forum}, booktitle = {AIAA Scitech 2020 Forum}, doi = {10.2514/6.2020-1006}, pages = {31 Seiten}, year = {2020}, language = {en} } @article{FingerBraunBil2020, author = {Finger, Felix and Braun, Carsten and Bil, Cees}, title = {Comparative assessment of parallel-hybrid-electric propulsion systems for four different aircraft}, series = {Journal of Aircraft}, volume = {57}, journal = {Journal of Aircraft}, number = {5}, publisher = {AIAA}, address = {Reston, Va.}, issn = {1533-3868}, doi = {10.2514/1.C035897}, year = {2020}, abstract = {Until electric energy storage systems are ready to allow fully electric aircraft, the combination of combustion engine and electric motor as a hybrid-electric propulsion system seems to be a promising intermediate solution. Consequently, the design space for future aircraft is expanded considerably, as serial hybrid-electric, parallel hybrid-electric, fully electric, and conventional propulsion systems must all be considered. While the best propulsion system depends on a multitude of requirements and considerations, trends can be observed for certain types of aircraft and certain types of missions. This Paper provides insight into some factors that drive a new design toward either conventional or hybrid propulsion systems. General aviation aircraft, regional transport aircraft vertical takeoff and landing air taxis, and unmanned aerial vehicles are chosen as case studies. Typical missions for each class are considered, and the aircraft are analyzed regarding their takeoff mass and primary energy consumption. For these case studies, a high-level approach is chosen, using an initial sizing methodology. Only parallel-hybrid-electric powertrains are taken into account. Aeropropulsive interaction effects are neglected. Results indicate that hybrid-electric propulsion systems should be considered if the propulsion system is sized by short-duration power constraints. However, if the propulsion system is sized by a continuous power requirement, hybrid-electric systems offer hardly any benefit.}, language = {en} } @inproceedings{FingerBraunBil2020, author = {Finger, Felix and Braun, Carsten and Bil, Cees}, title = {Comparative assessment of parallel-hybrid-electric propulsion systems for four different aircraft}, series = {AIAA SciTech Forum 2020, 06.01.2020 - 10.01.2020, Orlando}, booktitle = {AIAA SciTech Forum 2020, 06.01.2020 - 10.01.2020, Orlando}, doi = {10.2514/6.2020-1502}, pages = {15 Seiten}, year = {2020}, language = {en} } @article{FingerBraunBil2020, author = {Finger, Felix and Braun, Carsten and Bil, Cees}, title = {Impact of Battery Performance on the Initial Sizing of Hybrid-Electric General Aviation Aircraft}, series = {Journal of Aerospace Engineering}, volume = {33}, journal = {Journal of Aerospace Engineering}, number = {3}, publisher = {ASCE}, address = {Reston, Va.}, issn = {1943-5525}, doi = {10.1061/(ASCE)AS.1943-5525.0001113}, year = {2020}, abstract = {Studies suggest that hybrid-electric aircraft have the potential to generate fewer emissions and be inherently quieter when compared to conventional aircraft. By operating combustion engines together with an electric propulsion system, synergistic benefits can be obtained. However, the performance of hybrid-electric aircraft is still constrained by a battery's energy density and discharge rate. In this paper, the influence of battery performance on the gross mass for a four-seat general aviation aircraft with a hybrid-electric propulsion system is analyzed. For this design study, a high-level approach is chosen, using an innovative initial sizing methodology to determine the minimum required aircraft mass for a specific set of requirements and constraints. Only the peak-load shaving operational strategy is analyzed. Both parallel- and serial-hybrid propulsion configurations are considered for two different missions. The specific energy of the battery pack is varied from 200 to 1,000 W⋅h/kg, while the discharge time, and thus the normalized discharge rating (C-rating), is varied between 30 min (2C discharge rate) and 2 min (30C discharge rate). With the peak-load shaving operating strategy, it is desirable for hybrid-electric aircraft to use a light, low capacity battery system to boost performance. For this case, the battery's specific power rating proved to be of much higher importance than for full electric designs, which have high capacity batteries. Discharge ratings of 20C allow a significant take-off mass reduction aircraft. The design point moves to higher wing loadings and higher levels of hybridization if batteries with advanced technology are used.}, language = {en} } @article{FiedlerLaddClemensetal.2020, author = {Fiedler, Thomas M. and Ladd, Mark E. and Clemens, Markus and Bitz, Andreas}, title = {Safety of subjects during radiofrequency exposure in ultra-high-field magnetic resonance imaging}, series = {IEEE Letters on Electromagnetic Compatibility Practice and Applications}, volume = {2}, journal = {IEEE Letters on Electromagnetic Compatibility Practice and Applications}, number = {3}, publisher = {IEEE}, address = {New York, NY}, isbn = {2637-6423}, doi = {10.1109/LEMCPA.2020.3029747}, pages = {1 -- 8}, year = {2020}, abstract = {Magnetic resonance imaging (MRI) is one of the most important medical imaging techniques. Since the introduction of MRI in the mid-1980s, there has been a continuous trend toward higher static magnetic fields to obtain i.a. a higher signal-to-noise ratio. The step toward ultra-high-field (UHF) MRI at 7 Tesla and higher, however, creates several challenges regarding the homogeneity of the spin excitation RF transmit field and the RF exposure of the subject. In UHF MRI systems, the wavelength of the RF field is in the range of the diameter of the human body, which can result in inhomogeneous spin excitation and local SAR hotspots. To optimize the homogeneity in a region of interest, UHF MRI systems use parallel transmit systems with multiple transmit antennas and time-dependent modulation of the RF signal in the individual transmit channels. Furthermore, SAR increases with increasing field strength, while the SAR limits remain unchanged. Two different approaches to generate the RF transmit field in UHF systems using antenna arrays close and remote to the body are investigated in this letter. Achievable imaging performance is evaluated compared to typical clinical RF transmit systems at lower field strength. The evaluation has been performed under consideration of RF exposure based on local SAR and tissue temperature. Furthermore, results for thermal dose as an alternative RF exposure metric are presented.}, language = {en} } @incollection{FateriGebhardt2020, author = {Fateri, Miranda and Gebhardt, Andreas}, title = {Introduction to Additive Manufacturing}, series = {3D Printing of Optical Components}, booktitle = {3D Printing of Optical Components}, publisher = {Springer}, address = {Cham}, isbn = {978-3-030-58960-8}, doi = {10.1007/978-3-030-58960-8_1}, pages = {1 -- 22}, year = {2020}, abstract = {Additive manufacturing (AM) works by creating objects layer by layer in a manner similar to a 2D printer with the "printed" layers stacked on top of each other. The layer-wise manufacturing nature of AM enables fabrication of freeform geometries which cannot be fabricated using conventional manufacturing methods as a one part. Depending on how each layer is created and bonded to the adjacent layers, different AM methods have been developed. In this chapter, the basic terms, common materials, and different methods of AM are described, and their potential applications are discussed.}, language = {en} }